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REF3033: Output capacitor minimum ESR

Eddie Koh
Genius 10605 points

Part Number: REF3033

Datasheet, section 9.1 clearly stated that output cap is not required.

It does have a clause in section 9.1 for "special care when using low ESR caps and high capacitance"

Is there a guideline on what is "low ESR"? What value range is considered low for REF3033?

  • +1
    TI__Mastermind 47155 points

    Hi Eddie,

    Low ESR depends on the frequency.  See below:

    Based on the figure above, you will want to design your application such that you are at the minimum point of the ESR curve.  The ESR curve is generated by modeling a ceramic capacitor that includes the parasitic inductance and resistor.  The lowest point of the curve is called the resonant point where the impedance of the capacitor and the parasitic inductance have reached a minimum, which is roughly the equivalent to the resistor in the model (ESR).  It is my opinion that "low ESR" means anything less than 100mohms.

    Ben

  • 0 in reply to Ben C
    TI__Genius 10605 points

    Hi Ben,

    Given that most ceramic capacitors have an ESR of less than 100mOhms (and many have an ESR of 10mOhms or less), what is the maximum capacitance we should use on the output of the 3.3V reference? Does the maximum capacitance depend on the exact ESR i.e. does it change if the ESR is 10mOhms vs 80mOhms?

  • +1 in reply to Eddie Koh
    TI__Mastermind 47155 points

    Hi Eddie,

    It is difficult to just give you a number because adding more capacitance on the output increases the instability of the REF3033.  The best thing to do is to keep adding capacitance until the output gets unstable then add some resistance in series with the output capacitor.  Adding the resistor will increase the stability of the design.  

    Ben

  • 0 in reply to Ben C
    TI__Mastermind 47155 points

    Hi Eddie,

    Please let me know if you have any other questions.  If there are no further questions, please close the thread by clicking on "resolved".  Have a good weekend!

    Ben